Brouwer, Nathan
(2016)
APPLYING MULTILEVEL LONGITUDINAL MODELS TO PLANT DEMOGRAPHIC PROCESSES: NOVEL INSIGHTS INTO THE LONG-TERM IMPACTS OF INVASIVE SPECIES AND OVERABUNDANT HERBIVORES.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
Long-term, multi-factor studies are necessary to understand the population-level impacts and relative importance of species interactions. Such experiments produce data that are rich in detail but challenging to analyse. In my dissertation I have investigated the population-level impacts of two interactions, allelopathy and herbivory, by applying longitudinal statistical models to long-term experimental data. These data were collected during a decade-long investigation of impacts of white-tailed deer (Odocoileus virginianus) and an allelopathic invader (Alliaria petiolata) on forest herbs and trees.
There is great concern about the impacts of overabundant deer, but little is known about how quickly forests respond when deer abundance is reduced. Using biennial survey data I modeled changes in sapling abundance after deer exclusion. I found that Acer saccharum (sugar maple) but not other species exhibited signs of recovery in <7 years, but changes were obscured by density declines near the end of the study, likely due to self-thinning. Using meta-analysis I determined that other studies observed desired changes typically after ~20 years. Few, however, carry out frequent surveys and therefore likely miss important processes such as thinning.
Invasive plants are also widely considered to be an ecological problem. Small-scale experiments have established that allelopathic invaders can negatively impact plant fitness. To determine if an allelopathic plant has population-level effects, I modeled the impacts of Alliaria removal on the herb Maianthemum racemosum. While Alliaria removal benefits Maianthemum vital rates, changes take >5 years to appear. Broadening the analysis to compare the effects of deer and Alliaria on two additional herbs, I found that Alliaria impacts multiples species and vital rates, and that at times its effects can be as detrimental as deer browse.
Combining the power of experiments with sophisticated statistics, I have shown that plant-plant and plant-animal interactions can be similar in magnitude. Without longitudinal data and appropriate models, we would not have been able to characterize the effects of deer on saplings, or Alliaria on understory herbs, instead concluding that deer exclusion was not impacting forest regeneration and Alliaria removal not improving plant vital rates.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
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| Date: |
19 January 2016 |
| Date Type: |
Publication |
| Defense Date: |
29 October 2015 |
| Approval Date: |
19 January 2016 |
| Submission Date: |
24 November 2015 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
198 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Dietrich School of Arts and Sciences > Biological Sciences |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
deer, exclosure, ecology, mixed model, garlic mustard, Alliaria petiolata |
| Date Deposited: |
19 Jan 2016 15:44 |
| Last Modified: |
15 Nov 2016 14:31 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/26457 |
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